To investigate the motivations and psychological profiles of ultra-marathon runners using Myers-Briggs Type Indicator (MBTI), 52 Japanese subjects (mean age, 45.7 years; male, 76.9%) participated in the present study. It was found that 38.5% and 23.1% of the subjects begun ultramarathons because they wanted to run a longer distance than in usual marathons, and because of the influence of others, respectively. The motivations of each subject were categorized into achievement, social, and psychological reasons. Of the 52 subjects, 73.1%, 46.2%, 32.7%, and 26.9% reported that ultra-marathon running provides a sense of achievement (psychological reason), a challenge (achievement reason), the opportunity to extend current capabilities (achievement rea son), and the opportunity to socialize with other runners and meet people (social reasons), respec tively. According to the MBTI results, INFJ and ISFJ are the two dominant personality types in ultra-marathon runners. Running experience did not differ between INFJ/ISFJ and non-IFJ sub jects, indicating that the characteristics of INFJ/ISFJ subjects are not the results of the involve ment in ultra-marathons. In conclusion, this study suggests that Japanese ultra-marathon runners tend to be more introverted, make decisions based on their feelings, and control environment in an orderly manner than the Japanese normative population.